Modular pedicle screw system

ABSTRACT

Provided is a modular pedicle screw assembly which includes various components that may be configured in various manners so as to provide different functionalities to the pedicle screw assembly. This advantageously decreases surgery time, reduces repetitive and tedious surgical steps, and allows for streamlining inventory of expensive medical equipment. In one embodiment, a pedicle screw assembly includes a pedicle screw, a rod holding element, an insert, a rod, and a set screw. The insert may have a uniplanar configuration which allows movement of the insert, prior to final attachment, in a plane of motion. The insert may optionally have a monoaxial configuration which prevents movement of the insert. A method is also provided for securing a rod to a pedicle screw assembly. Also provided is an assembly tool for use in assembling a pedicle screw assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S. patentapplication Ser. No. 13/432,860, filed Mar. 28, 2012, entitled “ModularPedicle Screw System,” which claims priority to and is a continuation ofU.S. patent application Ser. No. 11/890,058, filed Aug. 3, 2007,entitled “Modular Pedicle Screw System,” now U.S. Pat. No. 8,167,912,which claims priority to U.S. Provisional Patent Application No.60/903,957, filed Feb. 27, 2007. Each of the above-identifiedapplications is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to medical devices. More particularly, theinvention relates to pedicle screw systems and methods for use in spinalfixation surgeries and therapies.

BACKGROUND OF THE INVENTION

Spinal surgery procedures often require securing various implants tovertebrae of the spine. One such implant is the pedicle screw and itsrelated components. Other components, such as rods, are then secured toindividual pedicle screw implants in order to provide a support orfixation function between and among neighboring vertebrae. Both the rodsand screws may have varying diameters and dimensions depending onpatient and therapeutic needs. Due to the complex curvature and anatomyof the spine it is difficult to align the bone screw and rod holderassembly with the rod, particularly when spanning multiple segments.Traditionally, this required extensive bending and test fitting of rodsto correctly approximate the rod holding portion of the pedicle screw.More recently, the polyaxial screw type has become widely available,which allows the rod receiving portion of the screw to pivot about thescrew head. The pivoting head allows the rod holder to interface withthe rod with only minimal rod contouring. These polyaxial screws are nowthe most common type of pedicle screw used today.

Current pedicle screw designs consist of several component partsincluding: 1) a threaded bone screw shaft which is anchored into thepedicle bone of the vertebrae 2) a rod holding member which is attachedto the head of the bone screw to receive a rod for stabilization of thespine, and 3) a set screw which interfaces with the top of the rodholder to compress the rod into the holder to form a stable construct.These components are assembled into two primary design types: monoaxialand polyaxial screw systems. The monoaxial screws typically have a fixedangular relationship between the bone screw and rod holder. These screwdesigns dictate that the rod is held perpendicular to the direction ofthe bone screw. While these designs are strong and stable, they make itdifficult to position the screw and rod properly and require a lot ofrod bending to correctly approximate the rod holder and rod. Polyaxialdesigns allow the rod holding member to pivot on the bone screw headsuch that the rod holder can properly interface with a rod that is notperfectly perpendicular to the direction that the bone screw isinserted. After the set screw is used to compress the rod into the rodholder, the polyaxial design will lock into place and no longer allowthe rod holder to pivot on the screw head.

Current designs suffer from some limitation in their functionality andthe manufacturing requirements to encompass the myriad variations ofparticular surgical approaches. For example, many companies must offerboth a monoaxial and polyaxial screw set, each with applications forspecific surgical procedures. Similarly, current designs rely on rodholders that are designed for one specific rod diameter. Thus, if amanufacturer wants to offer a system that can use both 5.5 mm and 6.0 mmrods, they must manufacture two different sized rod holders, and theymust manufacture both monoaxial and polyaxial variants of each sizeholder. This necessitates holding an inventory of parts in surgicalcenters, hospitals, and supply houses, many of which are rarelyutilized.

An additional shortcoming in current systems is the inability to createa uniplanar pedicle screw configuration that is able to pivot in onlyone plane of motion rather than the combined motions of the polyaxialdesign. A uniplanar design is useful in complex spinal reconstructivecases where multiple segments are spanned with stabilizing rods and whenlateral forces must be applied to a vertebrae to bring it into alignmentwith neighboring segments. With the traditional polyaxial designs, alateral force applied to the rod holding element will cause the rodholder to pivot on the bone screw head rather than rotate the vertebralbody.

Hence there has been identified a need to provide an improved pediclescrew device as well systems and methods of employing and utilizingpedicle screw assemblies. For example, it would be desired that animproved pedicle screw assembly reduce the necessary inventory ofexpensive medical components. The present invention addresses one ormore of these long felt but unmet needs.

SUMMARY OF THE INVENTION

The system proposed herein allows for a multipurpose pedicle screwassembly having multiple modular inserts. The combination of modularinserts allows the screw assembly to perform with differentfunctionalities that would be applicable with different surgicalprocedures. The selection of a particular kind of modular insert candetermine the assembly functionality. The modular pedicle screw assemblymay additionally incorporate a rod adapter that allows multiple sizedrods to be used with the same rod holding element. The differing screwconfigurations allow for a variety of screw functions that can all beachieved while using the same basic rod holding element, which is oftenthe most machining intensive component of any pedicle screw.

In one embodiment, and by way of example only, there is provided apedicle screw assembly that includes a pedicle screw, a rod holdingelement, an insert, a rod, and a set screw. The pedicle screw may have athreaded shaft and a flanged top. The rod holding element may define ascrew hole, an insert bearing area, a chamber, chamber walls, a saddlearea including a saddle area bottom point, and a threading area. Theinsert defines a bearing surface, side walls, and a receiving area; andthe insert may be positioned within the chamber such that the insertbearing surface contacts the rod holding element insert bearing area,and the insert side walls contact the chamber walls. The pedicle screwmay be positioned so that the screw shaft passes through the screw holeand the screw cap is positioned within the receiving area. The rod maybe positioned so as to rest on the upper surface of the insert. The setscrew, joined to the threading area of the rod holding element, securesthe rod to the upper surface of the insert. The rod holding element mayalso define a notch in the chamber walls, and the insert may define sidewalls having tabs. The insert may be positioned such that the tabs fitwithin the notches so as to aid in firmly securing the insert within therod holding element. The notch and tab may have a mutually fittingdovetail configuration. Optionally the insert may have a threadedreceiving area, and the bone screw may have a head with top threadsconfigured so as to mate with the threaded receiving area.

In a further embodiment, the assembly may also include a rod adapterattached to the set screw wherein the rod adapter includes a cradlingarea disposed around the rod so as to restrict movement of the rod. Therod adapter may further have a post with an inset, and the set screw mayfurther define a hole configured such that the post passes through thehole of the set screw. A locking ring affixed to the inset may securethe set screw to the rod adapter while allowing the set screw to rotaterelative to the rod adapter. Thus, the set screw and rod adapter areplaced atop the rod holding element as a single unit and not individualparts. The tabs on the rod adapting element also function as a guide toassist the surgeon in placing the set screw and ensure proper alignmentof the set screw with the rod holding element, thereby limiting thepotential for cross-threading of the set screw threads in the rodholding element.

In a further embodiment, also by way of example only, there is provideda medical kit that includes as components of the kit: a rod holdingelement configured to receive a rod with a first diameter, a rod adapterconfigured to adapt to a rod with a second diameter, a uniplanar insert,a monoaxial insert, and a set screw. The medical kit may further includeas optional elements a pedicle bone screw, which may be configured witha threaded top; and, as a further element, an insert configured to joinwith the threaded top of the pedicle bone screw. Additionally, themedical kit may also include a locking ring configured to secure the setscrew to the rod adapter so that the set screw can rotate relative tothe rod adapter; and a spacer configured to be disposed between the setscrew and the locking ring. The medical kit may also include a series oftools to aide in the placement of the screw system into the bone.

In still a further embodiment, and still by way of example only, thereis provided a method for securing a rod to a pedicle screw assembly, themethod includes the steps of: positioning an insert within a rod holdingelement; positioning a bone screw such that the head of the bone screwis disposed within a chamber defined by the rod holding element;positioning a rod within the rod holding element; and joining a setscrew to the rod holding element thereby securing the set screw, rod,insert, rod holding element, and bone screw in a final assembly. Themethod may also include the step of securing the bone screw in apatient's pedicle bone. The step of positioning an insert within a rodholding element may further include the step of aligning a tab on aninsert with a notch on the rod holding element. The method may furtherinclude the step of adjusting the position of the rod relative to thepedicle bone screw prior to final assembly, wherein the step ofadjusting the position may include moving a uniplanar insert within aplane of freedom. The method may further include the steps of: joining aset screw to an adapter such that the set screw can rotate relative tothe adapter; positioning the adapter around the rod; and the step ofjoining a set screw to the rod holding element may thereby secure theset screw, rod, insert, adapter, rod holding element, and bone screw ina final assembly.

Other independent features and advantages of the modular pedicle screwsystem will become apparent from the following detailed description,taken in conjunction with the accompanying drawings which illustrate, byway of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a rod holding element, according to anembodiment of the present invention;

FIG. 2 is a top view of a rod holding element, according to anembodiment of the present invention;

FIG. 3 is a partial cutaway view of a rod holding element, according toan embodiment of the present invention;

FIG. 4 is a perspective view of a monoaxial insert, according to anembodiment of the present invention;

FIG. 5 is a further perspective view of a monoaxial insert, with athreaded area, according to an embodiment of the present invention;

FIG. 6 is a further bottom perspective view of a monoaxial insert,according to an embodiment of the present invention;

FIG. 7 is a perspective view of a uniplanar insert, according to anembodiment of the present invention;

FIG. 8 is a further perspective view of a uniplanar insert, with athreaded area, according to an embodiment of the present invention;

FIG. 9 is a further perspective view of a uniplanar insert, with acorrugated bearing surface, according to an embodiment of the presentinvention;

FIG. 10 is an exploded front view of a pedicle screw assembly, accordingto an embodiment of the present invention;

FIG. 11 is a front view of a pedicle screw assembly, according to anembodiment of the present invention;

FIGS. 12A-12B are perspective views of bone screw embodiments for usewith embodiments of the present invention;

FIG. 13 is an exploded view of a threaded bone screw and threadeduniplanar insert, according to an embodiment of the present invention;

FIG. 14 is a perspective view of a threaded bone screw and uniplanarinsert, according to an embodiment of the present invention;

FIG. 15 is a perspective view of a rod adapter, according to anembodiment of the present invention;

FIG. 16 is an exploded view of a rod adapter and set screw assembly,according to an embodiment of the present invention;

FIG. 17 is a top view of a rod adapter and set screw assembly, accordingto an embodiment of the present invention;

FIG. 18 is an exploded view of a rod adapter and pedicle screw assembly,according to an embodiment of the present invention;

FIG. 19 is a front view of a rod adapter and pedicle screw assembly,according to an embodiment of the present invention;

FIG. 20 is a bottom perspective view of a rod holding element, accordingto an embodiment of the present invention;

FIG. 21 is an exploded view of a pedicle screw subassembly using anassembly tool, according to an embodiment of the present invention; and

FIG. 22 is a flow chart showing process steps in a surgical procedure,according to an embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The following detailed description of the invention is merely exemplaryin nature and is not intended to limit the invention or the applicationand uses of the invention. Furthermore, there is no intention to bebound by any theory presented in the preceding background of theinvention or the following detailed description of the invention.Reference will now be made in detail to exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Referring initially to FIGS. 1, 2, and 3 there is illustrated a firstembodiment of rod holding element 10. As further explained herein, rodholding element 10 functions as a structure with which variouscomponents cooperate in order to create a pedicle screw assembly. Thus,in one embodiment, rod holding element 10 includes various featureswhich are designed to cooperate with other pieces, and these features ofrod holding element 10 include rod cradle 11, insert notch 12, bearingsurface 13, and polyaxial head seating surface 14. The rod holdingelement 10 is versatile in that this single element can be used toassemble different kinds of pedicle screws including static screw,uniplanar screw, and polyaxial screw assemblies.

Rod holding element 10 is characterized by an opening 16. Opening 16 issized such that a tip and shaft of a bone screw (not shown) can passfrom an interior chamber area 15 of rod holding element 10 to theexterior of rod holding element 10. Rod holding element 10 furtherdefines chamber walls 17 which also define and limit chamber area 15. Aninsert, as explained further herein, can be placed within chamber area15.

Referring next to FIGS. 4, 5, and 6, there is illustrated an embodimentof a monoaxial insert 40. Monoaxial insert 40 includes bearing surface41, locking tabs 43, and in some embodiments, threading 44. Bearingsurface 41 is preferably designed so that bearing surface contacts rodholding element bearing surface 13 when monoaxial insert 40 is fullyplaced within rod holding element 10. Further, locking tabs 43 aredesigned so as to fit within the space defined by insert notch 12 of rodholding element 10. Preferably, locking tabs 43 are designed to fitwithin notch 12 so that when monoaxial insert 40 is fully assembled withrod holding element 10 the contact between locking tabs 43 and notch 12substantially restricts any movement of monoaxial insert 40. Asexplained further herein, locking tabs 43 and notch 12 may be configuredwith a mutually fitting dovetail shape. Thus, in effect, monoaxialinsert 40 is held to a single or static position within rod holdingelement 10.

FIGS. 4 and 5 illustrate embodiments of monoaxial insert 40 that do notinclude threading and that do include threading 44 respectively. As willbe understood by those skilled in the art, threading 44 such asillustrated in FIG. 5 can be used to secure a threaded bone screw head.However, the threading aspect of monoaxial insert 40 does not affect theabove-described position locking of monoxial insert 40 with respect torod holding element 10.

Referring now to FIGS. 7, 8, and 9, there is illustrated an embodimentof a uniplanar insert 70. It will be apparent that the overall shape andconfiguration of uniplanar insert 70 is similar, but not identical, tomonoaxial insert 40. For example, both monoaxial insert 40 and uniplanarinsert 70 have an external shape that allows them to slide into opening16 defined by rod holding element 10. However, in a point of difference,uniplanar insert 70 does not include locking tabs 43. Thus, for example,when disposed within opening 16, uniplanar insert 70 is not completelyrestricted from movement. Rather, when seated so that bearing surface 71of uniplanar insert contacts bearing surface 41 of rod holding element10, uniplanar insert 70 has two degrees of freedom so that it can have amovement when these bearing surface 71 and 41 move relative to oneanother. However, uniplanar insert 70 does not have a third degree offreedom in that side walls 75 of uniplanar insert are in substantialcontact with chamber wall 17 of rod holding element 10 and so restrictedin movement. Thus, with two degrees of freedom, uniplanar insert 70 canmove within a plane of motion relative to rod holding element 10.

Both a monoaxial insert 40 and a uniplanar insert 70 may share certaincommon features. For example both inserts 40 and 70 may include sidewalls 45 and 75. Further both inserts 40, 70 may also include an uppersurface 46 and 76. In a preferred embodiment, side walls 45, 75 andupper surface 46, 76 are substantially planar in configuration. Inserts40 and 70 may be configured such that when insert is placed withinchamber area, side walls 45 and 75 substantially contact chamber walls17 thereby restricting the movement of insert within rod holding element10. Additionally, both inserts 40 and 70 may include a hole (not shown)through which a bone screw (not shown) may pass; and they may alsoinclude a receiving area 47 and 77 shaped to receive the head of a bonescrew as explained further herein. Finally, both inserts 40 and 70 mayalso include threading for joining with a bone screw.

It will here be appreciated that the movement heretofore described forthe monoaxial insert 40 and uniplanar insert 70 assumes that bothinserts stay in a fully bottomed contact with rod holding element 10.Until final assembly of a pedicle screw assembly, both monoaxial insert40 and uniplanar insert 70 could be removed from opening 16 of rodholding element, a generally vertical movement (relative to thefigures). However, it will be appreciated that the placement ofmonoaxial insert 40 and uniplanar insert 70 within chamber 16accomplishes a preassembly which will ultimately lead to a finalassembly of a pedicle screw assembly. Thus, the potential movement ofremoving the inserts 40 and 70 has been ignored.

In a preferred embodiment, the insert 40 and 70 are convex andcylindrical in shape on their bearing surface 41, 71 where the insertcontacts the reciprocal bearing surface 13 of the rod holding element10. Thus the curvature of bearing surface 41, 71 of insert 40, 70preferably closely matches the curvature of rod holding element bearingsurface 13. The matching of these two surfaces forms, in one embodiment,a partial cylindrical bearing on which the insert can glide. If desired,bearing surfaces 41, 71 of inserts 40, 70 can be machined (or otherwiseformed) with corrugations or ridges 78 as shown specifically in FIG. 9.Ridge-like structures 78 can aide in locking the assembly into a desiredconfiguration when bearing surfaces are compressed together.

Referring now to FIGS. 10 and 11 there is illustrated an embodiment of afinal modular pedicle screw assembly, with FIG. 10 showing asemi-exploded view and FIG. 11 showing a fully assembled view. Pediclescrew assembly 100 includes bone screw 101, rod holding element 10,insert (uniplanar 70 or monoaxial 40), rod 105, and set screw 104. Inthe final assembly of FIG. 11, rod 105 is firmly held in position.

Comparing FIG. 10 to FIG. 11 illustrates further aspects of the modularpedicle screw embodiment 100. For example, it is noted that at the pointof assembly in FIG. 10, rod 105 has not yet come to a final position ofrest. Screw head 109 projects through insert 40, 70, and rod holdingelement 10 is still free to move generally along the length of screw101. Likewise, at this point of assembly insert 40, 70 is free to moverelative to rod holding element 10, as previously described. That is, auniplanar insert 70 can move in its plane of freedom; however themonoaxial insert 40 would be restricted, because of the tab/notch fit,except to move generally upward, with respect to the orientation of FIG.10. Rod 105 is also free to move relative to rod holding element 10.Thus, at this point of the assembly, a surgeon would typically bring theelements into alignment, as shown in FIG. 10; and then, using thefreedom of movement permitted, the surgeon could make what adjustmentsto that alignment the surgeon desires. And once the elements aresuitably aligned, the surgeon can begin to make the final assembly asfollows.

A surgeon would begin to press downward, relative to the orientation ofFIG. 10, for example on set screw 104. In a related fashion, the surgeoncould pull upward (again relative to the orientation of FIG. 10) on rodholding element 10. As a result of these movements, screw head 109passes into the receiving area 77 of insert 70, rod 105 passes into thesaddle area 11, and set screw 109 approaches threading area 19 of rodholding element 10. It is noted that the profile dimension of screw head109 is such that it can pass into receiving area 77 of insert 70 withoutsignificant resistance. As set screw 104 approaches threading area 19,set screw 104 may be rotated so that set screw threads 110 engagethreading area 19. The further rotation of set screw 104 continues tomove set screw 104 in a generally downward direction (relative to theorientation of FIG. 10), which movement brings bottom surface 14 of setscrew 109 into further contact with rod 105. The movement of rod 105likewise tends to move screw head 109 so that head 109 tends to movetowards receiving area 77. In this manner the further rotation of setscrew 109 continues to move the elements into an assembled configurationuntil the point of final assembly is reached as shown in FIG. 11.

It will also be appreciated by those skilled in the art that a modularpedicle screw assembly, preferably partially assembled, can also besecured in a pedicle bone prior to final assembly. For example, in onecommon practice, bone screw 101 can be assembled with rod holdingelement 10 and insert 40, 70. Bone screw 101 can then be inserted intothe patient's pedicle bone. Once bone screw 101 is anchored to thepatient's pedicle bone, the bottom of rod holding element 10 contactsthe bone which exerts an upward pressure on the rod holding element 10.However, the pressure exerted upwardly boy the bone against rod holdingelement 10 is not sufficient to prevent a uniplanar insert 70 fromtranslating within rod holding element 10. The final locking of theassembly occurs when rod 105 is added to the assembly and is presseddownward by set screw 104. It is further to be appreciated in thegeneral positioning and placement that surgeons are careful not to pullupwardly on these assemblies because in a degraded or diseased pediclebone the screws can be uprooted with such an upward force.

In a further embodiment, the placement of a modular pedicle screw can beassisted with the use of an assembly tool. Referring now to FIG. 21there is shown an exploded view of an exemplary embodiment of assemblytool 290 positioned with respect to rod holding element 10 and set screw104. In a preferred embodiment, assembly tool 290 includes pins 291which can align and join with reciprocal groove structures (not shown inFIG. 21) on rod holding element 10 as previously described. Assemblytool 290 further includes bit 292, which as illustrated can be hexshaped (or otherwise shaped) in order to fit within the reciprocal spaceon bone screw 127. A surgeon or surgical assistant may place assemblytool 290 into rod holding element 10 by aligning pins 291 with grooves.Further, the hex bit 292 is aligned with the bone screw 101, and setscrew 104 is then joined with rod holding element 10. Assembly tool 290preferably has a flat surface or top (not shown) so that as set screw104 is screwed into rod holding element 10, set screw 104 contacts theflat surface and thereby exerts a downward force on assembly tool 290.Additionally, assembly tool 290 preferably includes shoulder surface293. In one embodiment, shoulder surface 293 is substantially planar sothat as assembly tool 290 is pressed against insert 70 and bone screwhead 127, shoulder 293 tends to force bone screw head 127 to recedewithin the receiving area of insert 70. A surgeon can use a hex tool (orother kind of tool) to tighten set screw 104. As set screw 104 isfurther tightened, it ultimately pushes assembly tool 290 into abottomed out position. In this position, assembly tool 290 holds bonescrew 101 into a final assembled position relative to insert 40, 70 androd holding element 10. Taking advantage of the now positioned assemblytool 290, the surgeon can further apply torque to set screw 104 whichthereby serves to rotate the entire assembly, including bone screw 101.In this manner bone screw 101 along with the entire assembly can beplaced in a desired position relative to the patient's pedicle bone.

The assembly tool 290 illustrated in FIG. 21 provides advantages in theplacement and formation of pedicle screw assemblies over other knownmethods. In a first instance, assembly tool 290 prevents bone screw 101from moving out of axis with respect to rod holding element 10 whenbeing inserted in the patient's bone. This phenomenon of movement,sometimes referred to as toggling, is an undesirable feature of othersystems. Further, assembly tool 290 ensures that bone screw 101 remainsin a desired alignment with the driver being used to insert the screw.The driver/tool is inserted into the set screw and thereby rotates theentire assembly. Thus the torsional force applied by the surgeon to thedriver is advantageously aligned with bone screw 101 which allows thesurgeon to confidently proceed with bone screw 101 placement.

In one embodiment it is desired that the configuration of screw head 109closely matches the related configuration of receiving area 77 of insert70 (as receiving area 47 of insert 40). In this manner once screw head109 is fully assembled so as to drop fully into receiving area 77, theclosely matching configuration restricts the movement of screw head 109relative to insert 70. Thus, rod holding element 10, rod 105, and screw101 are also held into a desired position.

Referring now to FIG. 11 it is noted that the various elements have comeinto a final position and are significantly secured in that position.Rod 105 rests in rod cradle/saddle area 11, and the saddle arms 20 thatpartially define saddle area 11 are in contact with rod 105. Preferablythe width defined by saddle area 11 closely matches the diameter of rod105 such that rod 105 is not unduly restricted in moving to a bottomedposition within saddle area 11, and once in the bottomed position, asshown in FIG. 11, rod 105 is substantially restricted from side-to-sidemovement relative to the orientation of FIG. 11.

FIG. 11 also illustrates the point of interface 108 between rod 105 andupper surface 46 or 76 of insert 40 or 70. The point of interface 108indicates that rod 105 comes to final rest against surface 46, 76 ratherthan the bottom point 18 of saddle area 11 in the illustratedembodiment. (In an alternative embodiment discussed further herein, rod105 can rest in whole or part on bottom point 18 of saddle area 11). Itis further noted that the force exerted by rod 105 against insert 40, 70holds insert 40,70 firmly against bearing surface 13 of rod holdingelement 10, and thus insert 40, 70 is positioned with respect to rodholding element 10.

Referring now to FIG. 20, there is shown a further illustration of rodholding element 10. FIG. 20 shows a bottom view of rod holding element10, and in particular the figure illustrates screw hole opening 16. Aspreviously explained, screw hole opening 16 is configured so as to allowshaft 128 of a pedicle screw to pass therethrough. FIG. 20 alsoillustrates the further preferred embodiment in which screw hole opening16 is slightly oblong or elliptical in its shape, rather thansubstantially round, such that the dimension x 24 is greater thandimension y 26, each of which is substantially perpendicular to theother. This arrangement allows shaft 128 to have some limited linearmovement in the direction that aligns with dimension x 24.

The rod holding element with elliptical screw hole opening 16 may beadvantageously used with uniplanar insert 70. It is noted that dimensionx 24 is preferably aligned so as to present a particular configurationwith uniplanar insert 70 that would be positioned within rod holdingelement 10. The plane of movement that uniplanar insert 70 would move inis a plane of movement that is also generally aligned with dimension x24. Thus, when a bone screw passes through uniplanar insert 70, andshaft 128 of bone screw passes through screw hole opening 16, the planarmovement of uniplanar insert 70 will not be unduly impeded as shaft 128is also allowed some freedom of movement within the space of screw holeopening 16. As a further detail, it will be appreciated that dimension y26 should be configured with a length at least as large as the diameterof bone screw shaft 128.

Finally, while the preferred embodiment of screw hole opening 16 hasbeen illustrated in FIG. 20 as generally elliptical in shape, opening 16could take other configurations, such as, for example a generallyrectangular shape, or a generally rectangular shape with curved corners.It is also contemplated that the shape of opening 16 could follow agenerally rectangular shape, however a rectangle with somewhat curvedsides.

Referring now to FIGS. 12A-12B there are shown two varieties of screws,and at least these two screw varieties may be used with embodiments ofthe modular pedicle screw system. Screw 121, shown in FIG. 12B, includesa head 122 that has threads 123, and screw 121 may thus also be referredto as a locking threaded screw. Screw 125, shown in FIG. 12A, includes ahead 126 with no threads, and screw 125 may be referred to as anon-threaded screw or a flange-top screw. Screw 125 includes flange 127positioned on its head 126. Flange 127 is preferably shaped to match theconfiguration and area defined by receiving area 47, 77 of insert 40,70. The bone screws for use with the pedicle screw assembly alsotypically include a shaft 128, and shaft 128 may include shaft threads130. All threads on both the bone screws and set screw are exemplaryonly and do not represent the actual thread pitch and taper.

Referring now to FIGS. 13 and 14 there is illustrated an embodiment of athreaded screw 121 configured so as to be attached to a uniplanar insert70. Thus in the embodiment of FIG. 13 uniplanar insert 70 includes areciprocal threading 44 for bonding with the matching threads 123 ofthreaded screw 121. In the illustrated preferred embodiment, thethreaded head 123 screws into a uniplanar or monoaxial insert on theunderside of the insert, rather than a flanged head being inserted intothe receiving area from above. Essentially, the insert 40, 70 whenscrewed together with the pedicle screw 121 acts as a modular screwhead. The function remains unchanged from the monoaxial and uniplanardesigns. Insert 70 can be joined to threaded screw 121 by rotatinginsert 70 and/or threaded screw 121 so as to engage the reciprocalthreading 44 with threads 123. FIG. 13 illustrates threaded screw 121and insert 70 in an exploded view. FIG. 14 illustrates threaded screw121 joined with insert 70. FIG. 14 further illustrates how, in apreferred embodiment, the top 124 of threaded screw does not projectbeyond upper surface 76 of insert 70 to any significant extent, whichallows a rod (not shown) to lay substantially flush against uppersurface 70. Additionally, FIG. 14 illustrates how threaded screw 121 caninclude recessed area 129 for receiving a tool; and as known in the art,recessed area 129 may be configured as a socket with hexagonal walls (byway of example only) for receiving an Allen wrench. Although notillustrated, a nonthreaded screw may similarly include a recessed area.

Use of the locking threaded screw head embodiment can assist in lockingthe bone screw into the insert. The joinder achieved by the mutualthreading of the bone screw and the insert can increase the rigidity ofthe screw/insert assembly and help to prevent movement of the screwrelative to the insert. The locking threaded screw head can be useful inboth the uniplanar and monoaxial configurations. It is also preferredthat the locking threaded screw head embodiment be used with relativelylarger diameter bone screws.

It is here noted that the screw of FIGS. 13 and 14 may be advantageouslyused in certain surgical procedures. For example, some surgeons preferto affix a bone screw to a pedicle bone before any additional pediclescrew structure is attached to the bone screw. In such a technique thesurgeon generally has a clearer view of the pedicle bone while placingthe bone screw; additionally the technique allows the surgeon to shavebone material away from the area of the bone against which the rodholding element may ultimately be seated. Consistent with thistechnique, certain prior art systems, such as the Blackstone Iconsystem, are adapted so as to allow pedicle screw elements to snap ontothe bone screw head after the bone screw has been placed in the pediclebone. The above-noted embodiments of the pedicle screw system can alsobe assembled to the bone screw after the bone screw has been attached tothe patient. For example, insert 70 can be placed in rod holding element10. An assembly tool 290 and set screw 104, if desired, can hold theseitems in a desired relationship. Thereupon, this assembly can be screwedonto the threaded head 123 of bone screw 121.

Referring now to FIG. 15 there is illustrated an embodiment of rodadapter 200. As previously discussed, orthopedic therapies can call forrods having different qualities of strength and flexibility (among othercriteria), and this is achieved in one respect by specifying rods withdifferent diameters. To take two common examples in the industry, rodscan be used that have a diameter of either 5.5 mm or 6.0 mm. The modularpedicle screw assembly can accommodate rods with different diameters,from as small as 3.0 mm up to and including 6.5 mm, by use of rodadapter 200.

A preferred embodiment of rod adapter 200 generally includes a rodcradling portion 202, side wall 204, and rod adapter tab 205. In otherembodiment, rod adapter 200 can further include a post 206 with an inset207 for use with a locking ring device 209 as shown in FIGS. 16 and 17.Rod cradling portion 202 defines a generally semicircular surface with aradius adapted to substantially conform to the radius of the rod desiredto be used. For example, in one embodiment, it is desired to use the rodadapter 200 to secure rods with a 5.5 mm diameter. In such a situation,rod cradling portion 202 would have a substantially similar diameter.Further, it is preferred that the surface of rod cradling portion 202extend from a first end to the opposite end of rod adapter 200, as shownin FIG. 15, in order to provide a maximum surface area with which tosecure a rod.

As with the monoaxial insert 40, the tab 205 on rod adapter 200 isconfigured to fit within the reciprocal space defined by notch 12 on rodholding element 10. FIG. 10 illustrates in particular that embodiment inwhich tab 205 assumes a dovetail configuration, and in such a situation,notch 12 would likewise have a reciprocal dovetail shape in order toreceive tab 205. The function of this dovetail shape is to prevent thetop portion of the rod holding element from spreading apart laterallywhen the set screw is tightened against the rod, thereby imparting aforce between screw threads 19 and 104. Further, the improved alignmentof threads 19 and 104 created by the tabs 205 prevent cross-threadingand further mitigate the risk of rod holder head splay when the setscrew is tightened. Walls 204 are generally planar structures configuredto contact chamber walls 17 of rod holding element 10. In general, rodadapter 200 is configured to rest firmly within rod holding element 10.

Referring now to FIGS. 16 and 17, there is illustrated a subassembly ofrod adapter 200 and set screw 210. In the illustrated preferredembodiment, set screw 210 includes a recessed area 212. Within recessedarea 212 is an opening (not illustrated) which allows post 206 to passtherethrough. Recessed area 212 is generally configured so that when setscrew 210 is fully positioned on rod adapter 200; i.e., when the bottomsurface 213 of set screw 210 contacts upper surface 208 of rod adapter200, post 206 of rod adapter 200 projects through set screw openingsufficiently such that inset 207 of post 206 is exposed within therecessed area 212. In this manner locking ring 209 can be disposed so asto lock with inset 207 and around post 206. This positioning of lockingring 209 with post 206 then acts to restrict the movement of set screw210 away from rod adapter 200. However, locking ring 209 does notgenerally restrict the rotational movement of set screw 210 relative torod adapter 200.

It is also noted that recessed area 212 can define, in whole or part, aconfiguration for receiving a torsional tool such as a screw driver or ahex wrench. In the embodiment illustrated in FIG. 12, for example,recessed area 212 defines walls within the body of the set screw 212itself. The walls may define a hexagonal shape that can accommodate ahex wrench. A surgeon can thus dispose a tool within recessed area 212in order to forcefully manipulate set screw 210. Optionally, a spacer(not shown), such as a washer structure, can be disposed between lockingring 209 and the set screw 210.

The above subassembly of set screw 210 with rod adapter 200 is usefulduring surgical procedures in the following manner. Reference to FIG. 18is useful in understanding the following description. Using elementsearlier discussed, a surgeon has disposed a rod 105 within the chamberarea 15 defined by rod holding element 10. Further, rod 105 may beresting against an upper surface 46 of an insert such as a monoaxialinsert 40 or uniplanar insert 70. Portions of rod 105 may also restagainst the saddle bottom 18 defined by rod holding element 10. However,if rod 105, such as a 5.5 mm rod, is somewhat undersized for the givenrod holding element 10, rod 105 will experience some lateral movementwithin the rod holding element 10. It is generally desired to restrictthis rod movement as the pedicle screw reaches its final assembly, andhere is where the rod adapter subassembly comes into play. Rod adapter200 can now be positioned so that rod cradling portion 202 surrounds theupper portion of rod 105. As the rod adapter 200 is so positioned, tabs205 are aligned with notches 12. Then, as rod adapter 200 is moved in agenerally vertical downward position so as to fully engage the rod 105,set screw 210 (previously assembled with rod adapter 200) comes intocontact with threaded area 19 of rod holding element 10. Locking ring209 does not allow set screw 210 to dislodge from rod adapter 200;however, it does permit set screw 210 to rotate. Thus, the surgeon canmanipulate set screw 210 to rotate such that threads of set screw 210engage with the reciprocal threaded area 19 of rod holding element 10.This manipulation may be a hand manipulation or a tool-assistedmanipulation. Further, the surgeon can ultimately exert a desired amountof torque or tortional force on set screw 210 so that rod adapter 200forcefully engages with rod 105 and thereby securely holds rod 105 in adesired position. Further, the degree of contact between the surfaces ofrod 105 and the closely matching rod cradling portion 202 provide asufficient level of contact so that rod 105 cannot easily move laterallyrelative to rod adapter 200.

The subassembly of rod adapter 200 to set screw 210 is additionallyimportant to reduce the time needed during surgery. The use of such asubassembly, which can be constructed prior to surgery, eliminates theamount of time needed during surgery that would otherwise be required toput together these parts. Furthermore, it is generally desired to reducethe number of repetitive or fatiguing steps that must take place duringsurgery, and moving the subassembly to a time period outside thesurgical theater achieves that advantage. This advantage particularlyincreases in importance where multiple such screw assemblies will beemployed in the overall surgical procedure.

Referring now to FIG. 19 there is shown a further embodiment of a fullyconfigured pedicle screw assembly. FIG. 19 is also useful inillustrating one significant aspect of the function of rod adapter 200.As previously mentioned, rod adapter 200 is employed in those situationswhere the rod to be used during the surgical procedure is smaller thanwould normally fit in the saddle area 11 of rod holding element 10.Thus, FIG. 19 shows how the diameter of the saddle area 11 is indeedlarger than the diameter of rod 105 disposed within saddle area 11. Wereit not for rod adapter 200, rod 105 could more easily experience aside-to-side motion (relative to FIG. 19) within the saddle area 11 norwould the smaller diameter rod exert the necessary downward force ontothe insert when the set screw is tightened. However, rod adapter 200,shown with a diameter that closely matches rod 105, a diameter that isless than saddle area 11 diameter closely surrounds rod 105 and acts toprevent that movement. The rod adapter 200 also increases the surfacearea of contact with the superior aspect of rod 105 as compared to theflat bottom profile of the set screw alone. It should also be noted thata preferred embodiment would use a rod adapter 200 for all rod sizes,even those that fill the entire width of the saddle, to take advantageof the antisplay properties and increased area of contact discussedpreviously.

In a further embodiment, the modular pedicle screw system can beconfigured to allow for a dynamic stabilizing system. Referring again toFIG. 11 and FIG. 19 (the assembly with a rod adapter), it was noted thatin the final assembly of one preferred embodiment, rod 105 rests againstupper surface 46 or 76 of insert 40,70 rather than resting againstsaddle area 11 of the rod holding element 10. In such a scenario, oncerod 105 is inserted and the top set screw 104 is tightened, there willbe no motion of the screw 104 relative to rod holding element 10 due tothe compression created at the rod—insert interface 108. In the samemanner as a traditional polyaxial screw, the rod compresses the bearingsurface, insert, and screw head together to form a stable construct.However, with a simple modification of insert 40 and 70 (for example, byreducing the height dimension of insert slightly so that rod 105 doesnot compress insert 40, 70 but lies on the bottom point of saddle 11)the insert 40, 70 will remain able to pivot within the rod holdingelement 10. In a preferred embodiment of such dynamic stabilization, inthe final assembly rod 105 is also held at its upper position by the rodadapter. This can be useful in creating a dynamic system that allows forsome motion between the vertebrae that are spanned by rod 105, whichmore typically creates a rigid system.

There can be disadvantages to a rigid system in some instances that canbe ameliorated through a “dynamic stabilization”. For example, the useof rods that have flexible sections has been attempted. However,weakness of the flexible rod structure, movement in multiple degrees offreedom, and repeated stresses may lead to failure of the system andother complications. The modular system described herein allows the rodholder to be dynamic, rather than the rod itself. From a biomechanicalperspective, it is advantageous to dynamize the rod holding elementbecause the degrees of freedom in the dynamic system can be limited bychoosing the appropriate insert and the allowed motion can be alignedwith the natural motion of the spinal segment being stabilized.

In a further embodiment, an insert may be eliminated altogether as aseparate piece in the assembly. In this embodiment, the head of the bonescrew is machined in the same shape, or substantially the same shape, aseither the uniplanar insert 70 or monoaxial insert 40. Essentially twopieces are replaced with a single piece, which may further lead to timesavings during surgery procedures and cost savings from machining fewerparts in total. Functionally the combined screw insert assembly issimilar to the previously enumerated monoaxial and uniplanar designs butthe machining process and parts are different.

As has been mentioned, embodiments of the modular pedicle screw systemcan be used with various surgical techniques and procedures as practicedin orthopedic surgery. Referring to FIG. 22, there are listed someexemplary steps that may be followed in one such method of usage. Instep 321, a surgeon may begin the process by creating a subassemblycomprising a bone screw, insert, assembly tool, rod holding element, andset screw. This advantageously secures the bone screw in a desiredrelationship relative to the rod holding element. Further, the bonescrew can then be set in the patient's pedicle bone, step 322, byapplying a hand tool to the set screw, which, because of the assemblytool's linkage with the bone screw, applies torsional force to the bonescrew. It will be appreciated that in other embodiments, such as theembodiment described previously in which the bone screw includes topthreading, the bone screw may be applied directly to the pedicle bone.Step 323 calls for positioning an insert within the rod holding element.This step may occur as part of the preassembly construction, step 321 orafter the bone screw has been positioned, depending on the optionselected. Step 324 which calls for aligning a tab on the insert with anotch on the rod holding element is an optional step in the overall stepof placing the insert if the insert is equipped with such a structure.In step 325, the head of the bone screw is positioned such that the headof the bone screw is disposed within the rod holding element chamber.Again, depending on the surgical option, this may occur in constructingthe preassembly of step 321. Optionally, this step may occur after thebone screw has been placed in the patient.

In step 326 a rod is placed within the rod holding element. It will herebe appreciated that in those embodiments that use an assembly tool, thesubassembly that includes the assembly tool must be disassembled (theset screw must be removed) and the assembly tool must be removed. Oncethe assembly tool has been removed, the rod may be placed within the rodholding element. Thus, placement of the rod within the overall assemblytypically takes place after placement of the bone screw. Once the rodhas been positioned, the final assembly can be secured; i.e., the setscrew can be joined to the rod holding element. And, as previouslydescribed, tightening of the set screw pushes against the rod, which inturn pushes against the insert until a desired tension is obtained.Note, that if dynamic tensioning is desired, the rod may also contactthe lower saddle portion of the rod holding element.

Referring again to FIG. 1, it is to be noted that in the preferredembodiment, rod holding element 10 includes flats 21 on an outer surfaceof rod holding element 10. Flats 21 are typically a generally flat area,on mutually opposing sides of rod holding element 10, configured forreceiving any number of surgical tools. By way of example, a wrenchcould be applied to the flats 21 to rotate the rod holding elementdirectly. Similarly, as would be familiar to those skilled in the art ofspinal fixation devices, a rod reducing tool could be placed on theflats as a secure anchoring point for a tool to forcefully guide the rodinto the rod cradle when alignment by hand is difficult. Such amanipulation of rod holding element 10 or rod 105 may be useful atvarious stages of surgery rather than manipulating some other element ofthe system.

As previously mentioned, a dovetail configuration of mutually assembledelements can be useful in assembling and locking pieces into a desiredarrangement. Thus, rod holding element 10 can be configured with adovetailed notch 12 and rod adapter 200 can be configured with adovetailed tab 205 where both tab 205 and notch 12 are mutuallyconfigured to match each other. Additionally, the monoaxial insert 40can be configured with a dovetailed locking tab 43 that alsoreciprocally matches the dovetailed configuration of notch 12. Thisarrangement of elements is useful not only for firmly engaging pieces ina desired configuration; it can also help to prevent the head of the rodholder 10 from tending to splay outward when, as the set screw 210 istightened, it exerts a force on the elements that tend to push outwardlyagainst chamber walls 17 of rod holding element. The illustratedconfiguration of tabs and notches, where rod holding element notch 12has a closed rather than open configuration, helps to resist thatoutward force. It is thus to be noted that the dovetail configurationdescribed above with respect to the rod adapter 200 can be applied toother elements in the various pedicle screw embodiments, and is notlimited to that single application.

Attachment means other than the described set screw 210 may also be usedwith the various pedicle screw embodiments described herein. For examplean external nut can be applied as the fastening and tighteningmechanism. Similarly, helically cut threads, which reducecross-threading and head splay, may also be employed as a fastening andtightening mechanism.

It will be appreciated by those skilled in the art that a variety ofthread patterns are known for use with pedicle screws. Thus, where acertain kind of thread pattern has been illustrated with a particularelement, such as the threads by which the set screw is joined to the rodholding element or the thread pattern by which the pedicle screw itselfis lodged in the bone, the illustrated thread pattern is presented forillustrative purposes only. The embodiments of the modular pedicle screwsystem can be used with a variety of different screw patterns anddesigns.

Additionally, bone screws may also vary beyond their thread pattern, andthe embodiments described herein are generally useful with othervarieties of bone screw than the particular examples described. Morespecifically, certain bone screws may have a cannulated design to assistin surgical placement and navigation to the correct location andangulation. Such cannulated bone screws may also be used with thedescribed embodiments of the invention.

The materials that may comprise the various elements of the modularpedicle screw assembly are now discussed. Generally, any suitablematerial used for orthopedic implants may be employed. Particularly,those materials known to a practitioner skilled in the art that havebeen used for prior art pedicle screw designs may also be used inconstructing the elements of the invention embodiments described herein.The rod holding element, the rod adapter element, and the insert elementmay likewise be fabricated of these same materials. Thus, by way ofillustrative example only, titanium and stainless steel alloys may beused in fabrication.

While the invention has been described with reference to a preferredembodiment or embodiments, it will be understood by those skilled in theart that various changes may be made and equivalents may be substitutedfor elements thereof without departing from the scope of the invention.In addition, many modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to a particular embodiment disclosedas the best mode contemplated for carrying out this invention, but thatthe invention will include all embodiments falling within the scope ofthe appended claims.

What is claimed is:
 1. A pedicle screw assembly comprising: a rodholding element, wherein the rod holding element defines a screw hole, abeating area, a chamber, a saddle area, a threading area, and a notch; asingle-piece bone screw having a threaded shaft and a head, the headhaving an insert portion that defines a bearing surface, an uppersurface, a receiving area, and a tab, wherein the insert portion ispositioned within the chamber of the rod holding element such that thebearing surface contacts the bearing area of the rod holding element andthe tab fits within the notch of the rod holding element, wherein thebone screw is disposed such that the shaft passes through the screw holeof the rod holding element; a rod disposed to rest on the upper surfaceof the insert portion of the bone screw; a set screw joined to thethreading area of the rod holding element so as to secure the rod to theupper surface of the insert portion of the bone screw; and a rod adapterattached to the set screw, wherein the rod adapter comprising a tab anda cradling area disposed around the rod so as to restrict movement ofthe rod, wherein the notch of the rod holding element has a dovetailconfiguration, wherein the tabs of the rod adapter and the insertportion of the bone screw have dovetail configurations that arereciprocally shaped relative to, and configured for complementaryreceipt within, the notch, and wherein the notch and the reciprocallyshaped tabs are configured to prevent the rod holding element fromspreading apart laterally as the set screw is tightened against the rod.2. The assembly according to claim 1, wherein the rod adapter furthercomprises a post with an inset, wherein the set screw further defines ahole such that the set screw is positioned so that the post passesthrough the hole of the set screw, and wherein the assembly furthercomprises a locking ring disposed so as to secure the set screw to therod adapter while allowing the set screw to rotate relative to the rodadapter.
 3. The assembly according to claim 1, wherein the saddle areaof the rod holding element defines a bottom point, and wherein the rodcontacts the upper surface of the insert portion of the bone screw butdoes not contact the bottom point of the saddle area.
 4. The assemblyaccording to claim 1, wherein the saddle area of the rod holding elementdefines a bottom point, and wherein the rod contacts the bottom point ofthe saddle area.
 5. The assembly according to claim 1, wherein the rodholding element further defines chamber walls; and wherein the insertportion of the bone screw also defines side walls such that the sidewalls of the insert portion make substantial contact with the chamberwalls so as to partially restrict movement of the insert portion withinthe chamber of the rod holding element.
 6. The assembly according toclaim 1, wherein the rod holding element further defines flats thatpermit manipulation of the rod holding element by a tool.
 7. Theassembly according to claim 1, wherein the set screw further defines atool receiving area.
 8. The assembly according to claim 1, wherein thebone screw further defines a tool receiving area.
 9. The assemblyaccording to claim 1, wherein the insert portion of the bone screw is amonoaxial insert portion that is held in a single position within therod holding element.
 10. The assembly according to claim 1, wherein theinsert portion of the bone screw is a uniplanar insert portion that isconfigured to move within a plane of motion relative to the rod holdingelement.
 11. The assembly according to claim 10, wherein the bearingsurface of the insert portion of the bone screw is corrugated.
 12. Amethod for securing a rod to a pedicle screw assembly, the methodcomprising: positioning an insert portion of a single-piece bone screwwithin a chamber of a rod holding element, the rod holding elementdefining a screw hole, a bearing area, a chamber, a saddle area, athreading area, and s notch, the insert portion of the bone screwdefining a bearing surface, an upper surface, a receiving area, and atab, wherein the insert portion of the bone screw is positioned withinthe chamber of the rod holding element such that the bearing surface ofthe insert portion contacts the bearing area of the rod holding elementand the tab fits within the notch of the rod holding element, andwherein the bone screw is disposed such that the shaft passes throughthe screw hole of the rod holding element; positioning a rod within therod holding element, wherein the rod rests on the upper surface of theinsert portion of the bone screw; joining a set screw to the threadingarea of the rod holding element; and joining the set screw to a rodadapter such that the set screw can rotate relative to the rod adapter,wherein the rod adapter comprises a tab and a cradling area; positioningthe cradling area of the rod adapter around the rod; tightening the setscrew against the rod to secure the rod against the upper surface of theinsert portion of the bone screw, wherein the notch of the rod holdingelement has a dovetail configuration, wherein the tabs of the rodadapter and the insert portion of the bone screw have dovetailconfigurations that are reciprocally shaped relative to, and arereceived within, the notch, and wherein the notch and the reciprocallyshaped tabs prevent the rod holding element from spreading apartlaterally as the set screw is tightened against the rod.
 13. The methodaccording to claim 12, further comprising securing the bone screw in apatient's pedicle bone.
 14. The method according to claim 13, furthercomprising adjusting the position of the rod relative to the bone screw.15. The method according to claim 14, wherein the insert portion is auniplanar insert portion, and wherein the uniplanar insert portion ismoved within a plane of freedom to adjust the position of the rodrelative to the bone screw.
 16. The method according to claim 12,wherein the rod is secured such that the rod contacts the upper surfaceof the insert portion of the bone screw but does not contact a bottompoint of the saddle area of the rod holding element.
 17. The methodaccording to claim 12, wherein the rod is secured such that the rodcontacts a bottom point of the saddle area of the rod holding element.